Regulation and Control Flashcards
What is homeostasis?
A function of control systems in mammals to maintain a stable internal environment.
Why is constant temperature important?
Low temperatures slow metabolic reactions and high temperatures cause denaturation of proteins (enzymes)
Why is constant amount of water important?
Lack of water in tissue fluid causes water to be drawn out of cells (osmosis), slowing/stopping metabolic reactions. Too much water entering the cell can cause swelling/bursting.
Why is constant amount of glucose important?
Lack of glucose slows/stops respiration, depriving cell of energy source. Too much glucose may draw water out of cells by osmosis.
What is negative feedback?
A control loop used in control mechanisms in which a RECEPTOR picks up information about regulated parameter (INPUT), resulting in action by the EFFECTOR (OUTPUT).
What is excretion?
Elimination from the body of waste compounds produced during the metabolism of cells, including, for a human, carbon dioxide (excreted through the lungs) and urea (excreted through the kidneys in urine).
Why is removing nitrogenous waste products important?
Urea is produced by the liver from excess amino acids. There is more protein than needed, and the excess cannot be stored in the body as it is toxic.
Why is removing carbon dioxide important?
Carbon dioxide is not needed by the body, and produced by almost every cell. Transported from cells to lungs in bloodstream, diffuses into the alveoli and excreted when we breathe out.
What is a REFLEX ARC?
The pathway along which impulses are carried from a receptor to an effector without involving ‘conscious’ regions of the brain. e.g. in a spinal reflex arc, the impulse is carried from sensory neurone to intermediate neurones to motor neurones inside the spinal cord. In spinal cord, impulse will also be passed onto brain through other neurones. The effector responds to stimuli before any voluntary response. Useful for danger signals (eg hot object)
What are nerve impulses?
Very brief changes in the distribution of electrical charge across the plasma membrane, caused by movement of Na and K ions in/out of the axon.
What is the potential difference at RESTING POTENTIAL?
-65mV. The inside of the axon has a slightly negative electrical potential compared to the outside.
How is RESTING POTENTIAL maintained?
It is produced and maintained by the SODIUM-POTASSIUM PUMP in the plasma membrane of the axon. NA+ are picked up from cytoplasm inside axon by a CARRIER PROTEIN, and carried OUT. At the same time, K+ are brought into cytoplasm by external fluids. Both processes move ions against their concn gradient and require energy (hydrolysis of ATP). 3Na+ are removed for every 2K+ brought into cell and K+ diffuses out much faster than Na+ diffuses in, resulting in xs of +ve outside memb compared to inside.
What causes an ACTION POTENTIAL?
Electric current used to stimulate axon causes VOLTAGE-GATED CHANNELS (just the sodium channels) to open in the plasma memb to allow Na+ diffusion back into axon. The membrane is DEPOLARISED (less -ve tha before) and beings to build up positive charge.
What is the potential difference at ACTION POTENTIAL?
+40mV
How is the axon REPOLARISED? (2)
1) When potential difference reaches +40mV, SODIUM VOLTAGE GATED CHANNELS close and POTASSUM VOLTAGE GATED CHANNELS open. K+ diffuses out of the axon, removing +ve charge inside, beginning to return potential difference to normal. Membrane briefly becomes more -ve than normal at resting potential due to so many K+ ions diffusing out (REFRACTORY PERIOD). 2) POTASSIUM voltage gated channels close, and the SODIUM POTASSIUM PUMP begins restoring normal distribution of Na+ and K+ (resting potential).
How is an ACTION POTENTIAL transmitted along a neurone?
An action potential at any point on an axon’s plasma memb triggers production of action potential on either side. 2) causes a ‘local circuit’ to be set up between depolarised region and resting regions on either side. Na+ ions flow sideways inside axon, away from +vely charged region towards -ve regions on either side, depolarising these regions and generating an action potential.
How does the MYELIN SHEATH speed up the rate of conduction?
By insulating the axon membrane, so action potentials travel at up to 100m/s. Na and K ions cannot flow through myelin so action potentials only occur at the NODES OF RANVIER.
What is SALTATORY CONDUCTION?
When action potentials ‘jump’ from one node of Ranvier to the next due to myelinated areas, speeding transmission up by 50x.
Why is the REFRACTORY PERIOD important?
A ‘new’ action potential is only generated ahead of point of stimulation as region behind is in its REFRACTORY PERIOD ( Still be recovering from it’s action potential, and Na+ and K+ distribution will not yet be normal.)
How do RECEPTOR CELLS function?
They convert energy in one form (heat, light, sound) into energy in an electrical impulse in an neurone. They can be individual cells, or simply the ends of sensory neurones.
What is a PACINIAN CORPUSCLE?
It is found in the dermis of skin and contains the ending of a sensory neurone surrounded by several layers of connective tissue (CAPSULE, no myelin).
How does a PACINIAN CORPUSCLE function?
When pressure is applied, the CAPSULE is pressed out of shape and deforms nerve ending inside. This causes NA and K CHANNELS to open, allowing Na+ in and K+ out, depolarising membrane, causing increased positive charge in axon (RECEPTOR POTENTIAL). Above a pressure threshold, an ACTION POTENTIALS are initiated. (more pressure=higher frequency)
What is a TRANSMITTER SUBSTANCE?
Chemicals which pass action potential signals across synapses.
What is the PRESYNAPTIC NEURONE?
The neurone the transmitter substance is released from.
Describe GLOMERULAR FILTRATION (3)
1) Fenestrations in capillary endothelium are large and let dissolved substances in blood plasma to move into the capsule (down the WP gradient) whie the basement membrane stops any large proteins from getting through (filters out erythrocytes etc.).
2) In gomerular capillaries, blood pressure is relatively high due to the wider diameter of afferent arteriole (to) compared to efferent arteriole (from), raising WATER POTENTIAL of blood plasma above WP of contents of Bowman’s capsule.
3) Even though concentration of solutes in blood is higher than solutes inside Bowman’s capsule (due to plasma proteins too big to get through), which lowers the WP of the blood, the effect of differences in pressure outweigh the effect of differences in solute concn.
Describe SELECTIVE REABSORPTION in the PROXIMAL CONVOLUTED TUBULE. (4)
1) Basal membranes (nearest blood) of cells lining the tubule ACTIVELY TRANSPORT Na+ out of the cell, into the blood.
2) Na+ from tubule filtrate PASSIVLEY diffuses back thourgh CARRIER PROTEINS in the membrane. These have several kinds, which transport different substances (eg glucose) as well as Na+ at the same time. The concn gradient for Na+ provides enough energy for glucose molecules to be tken up the cell, and into the blood. All glucose in glomerular filtrate is transported out of the tubule, ino the blood.
3) Water follows these substances out of the tubule through osmosis, down the concn gradient.
4) Urea (small) is also reabsorbed by its passive diffusion. Uric acid and creatinine are not.
